Slip casting is an ancient art. Generally in this art, a ceramic material suspended in a vehicle is poured into a suitable mold. The vehicle is drawn out of the casting slip and a consolidated casting is left behind in the mold. Normally, such a consolidated casting has a low green strength. Green strength is defined as the flextural strength exhibited by an object after completion of its forming process.
The prior art has taught that binders can be added to casting slips to increase the green strength of the resulting casting. Green strength is required in the casting so that the casting may be removed from the mold in which it has been formed and thereafter handled. However, by adding binders to a casting slip, very often the final green density of the completed article is much lower than that produced from slips having no binder additive. This comes about because the binder takes up space during consolidation of the cast object and, upon subsequent burn out of the binder, the elimination of the binder produces a void. A binder addition can also alter the mechanism for slip suspension thereby forming lower density articles. Such a reduction of density because of the use of a binder system is not desirable in articles in which one desires to obtain a maximum final density.
The process set forth herein has the ability of producing a high green strength casting without the use of direct binder materials in the slip and without sacrificing the highest possible green density of the casting. In the process set forth herein, at least a portion of the mold material used in forming the shape of the casting is also instrumental in increasing the green strength of the casting.
It is the principal object of this invention to provide a method by which maximum density may be obtained in a slip cast article but yet the article will have a green strength greater than the article would have if it was formed only of consolidated casting material.